achievement age

the level of educational development of an individual as determined by an achievement test and based on a comparison of the examinee's score with the average score of individuals of the same chronological age.

achievement age a·chieve·ment age (ə-chēv'mənt)n. The level of an individual's educational accomplishment as measured by standard achievement tests and expressed as the age in years of a child for whom the total score would be an average score.